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I have the choice between:

  1. 35x35mm GPS antenna 71% efficiency glonass, tested on 70x70 GND plane 60% gps
  2. 25x25mm GPS antenna 83% GPS, 84% glonass, tested on 50x50 GND plane

I have read somewhere by a GPS manufacturer that antenna size is more important than efficiency but I feel doubtful about that. Would like to hear your thoughts.

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  • \$\begingroup\$ I would have to see the datasheets of both antennas to really be able to decide which one might have better reception. It can be as simple as that the efficiency measurements aren't done in exactly the same way making the "better" antenna look "worse". Regarding the size of the antenna, I would only care that the antenna fits inside my product. How "good" the antenna is I can read in the datasheet. \$\endgroup\$ – Bimpelrekkie Apr 29 '19 at 12:43
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    \$\begingroup\$ Nothing beats actual testing in real live conditions :-) \$\endgroup\$ – jcaron Apr 29 '19 at 12:50
  • \$\begingroup\$ What are the Sensitivity ratings of those units? Such as "Receive Sensitivity -185 dbw minimum" with these Garmin units static.garmin.com/pumac/GPS_18x_Tech_Specs.pdf or static.garmin.com/pumac/GPS_16x_tech_specs.pdf There are smaller units, but with no tech data posted buy.garmin.com/en-US/US/p/pn/010-10702-00 \$\endgroup\$ – CrossRoads Apr 29 '19 at 13:39
  • \$\begingroup\$ jcaron beat me to it. If it really matters, make a board with both on there and test. \$\endgroup\$ – danmcb Mar 29 at 12:04
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In principle bigger is better but we are talking about a GHz signal here (I don't remember the exact frequency); since we are not talking about short antennas (in the electrical sense) I think that matching and a proper lobe would be more important than raw size.

I guess that being bigger should have a slightly better gain

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Everything else being equal (same type of antenna, same gain...), a 35x35 mm antenna should receive nearly twice the power compared to a 25x25 mm antenna. That means that even if the smaller one is slightly more efficient, the larger one still results in a much higher output power.

But there are lots of other parameters that may affect the performance of antennas. Your best bet is to test both antennas in the same conditions (preferably in a wide set of conditions) to see which one actually performs best (in each case, possibly).

Of course, beyond the performance of the antenna, there may be other considerations such as overall size, cost, ease of integration, etc. As noted in your quote, the measurements are based on the use of a pretty large ground plane, which may or may not fit in your application, for instance.

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    \$\begingroup\$ I don’t know why this was down-voted without comments (-1) but does the ref. Gnd area doubling translate into double the power for near-field fringe effects when most of the EH field is concentrated around the feed point (?) Ref pls... \$\endgroup\$ – Tony Stewart EE75 Mar 29 at 12:21

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